104 THE PROTEIN SUBSTANCES. 



close to the nucleoproteins by their content of phosphorus, but differ 

 from these in not yielding any purine bases on cleavage. It has not 

 yet been found possible to obtain from the neucleoalbumins any proteid- 

 free pseudonucleic acids corresponding to the nucleic acids, but only 

 acids rich in phosphorus, which always give the proteid reactions (LEVENE 

 and ALSBERG, SALKOWSKI, REH 1 ). For this reason the nucleoalbumins 

 cannot be classed as compound proteins. In peptic digestion a proteid 

 rich in phosphorus can be split off from most nucleoalbumins, and this 

 has been called para- or pseudonuclein. The claim made that the pseu- 

 donuclein is a combination of proteid with metaphosphoric acid has 

 been shown to be incorrect by the investigations of GiERTz. 2 The nucleo- 

 albumins always seem to contain some iron. 



The separation of pseudonuclein in peptic digestion is no doubt characteristic 

 of the nucleolabumin group, but the non-appearance of the pseudonuclein pre- 

 cipitate does not entirely exclude the presence of a nucleoalbumin. The extent 

 of such a formation is dependent upon the intensity of the pepsin digestion, the 

 degree of acidity, and the relation between the nucleoalbumins and the digestive 

 fluids. The separation of a pseudonuclein may, as shown by SALKOWSKI, 

 not occur even in the digestion of ordinary casein, and WROBLEWSKI did not 

 obtain any pseudonuclein at all in the digestion of the casein from human milk. 

 WIMAN 3 has also shown in the digestion of vegetable nucleoalbumin that the 

 obtainment of considerable pseudonuclein or none is dependent upon the way in 

 which the digestion is performed. The most essential characteristic of this group 

 of proteids is that they contain phosphorus, and that the purine bases are absent 

 in their cleavage products. 



The nucleoalbumins are often confounded with nucleoproteins and 

 also with phosphorized glucoproteins. From the first class they differ 

 by not yielding any purine bases when boiled with acids, and from the 

 second group by not yielding any reducing substance on the same treat- 

 ment. The best studied member of this group is the casein of milk, 

 which will be discussed in detail in a subsequent chapter (XIV). 



Lecithalbumins. In the preparation of certain protein substances, 

 products are often obtained containing lecithin, and this lecithin can 

 be removed only with difficulty or incompletely by a mixture of alcohol 

 and ether. Ovovitellin (Chapter XIII) is such a protein body con- 

 taining considerable lecithin, and HOPPE-SEYLER considers it a combina- 

 tion of proteid and lecithin. Similar substances occur in fish-eggs. 

 These last lecith albumins often have the solubilities of the globulins, 



1 Levene and Alsberg, ibid., 31; Salkowski, ibid., 32; Levene, ibid., 32; A. Reh, 

 Hofmeister's Beitrage, 11. 



2 Giertz, Zeitschr. f. physiol. Chem., 28. 



3 Salkowski, Pfluger's Arch., 63; Wroblewski, Beitrage zur Kenntnis des Frauen- 

 kaseins, Inaug.-Diss., Bern, 1894; Wiman, Upsala Lakaref. Forh. (N. F.), 2. 



